ul.arena{
    padding: 0;
    list-style: none;
    overflow: hidden;
    margin: 20px auto;
    width: 390px;
}
ul.arena li{
    height: 150px;
    width: 150px;
    border: 1px solid yellow;
    float: left;
    margin: 0 20px;
    background: #000000;
}
ul.arena.cards{
    overflow-x: auto;
    overflow-y: hidden;
    height: 152px;
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    width: auto;
}